Color image sensors are used in a variety of electronic devices which capture color image data and convert the optical image to electrical signals. For example, color image sensors are commonly used in digital cameras, including standalone still image and video cameras, as well as multi-function devices with camera functions, such as cellular phones, smart phones, personal digital assistants, web cams, laptop computers, and the like. The term “camera”, as used herein refers to any such electronic imaging device.
A common form of color image sensor has an array of picture elements (pixels), each covered by a respective color filter. For example, the color filters may be arranged in a Bayer pattern, having alternating red-green and green-blue rows. The red filters pass red light and ideally block blue and green light. The green filters pass green light and ideally block blue and red light. The blue filters pass blue light and ideally block red and green light.
However, a variety of factors may result in crosstalk between neighboring colored pixels and between colors. For example, spectral crosstalk may result from imperfect blocking of green or blue light by a red filter, imperfect blocking of red and blue light by a green filter, or imperfect blocking of red and green light by a blue filter. Optical crosstalk occurs when a given pixel receives light that should ideally only reach a nearby pixel. This may occur, for example, if the incoming light has a non-perpendicular light incidence angle. Other sources of optical cross talk include light scattering and reflection at color filter array (CFA) and micro-lens boundaries, interconnect metal wires, and light diffraction due to the small size of each color filter pitch. Additionally, there is electrical cross talk, caused by photo-carrier diffusion in the silicon substrate beneath pixels of different colors.
Color crosstalk results in degradation of sensor spatial resolution. Color information on one pixel is contaminated by information of its neighbors. This results in degradation of color fidelity.